Recently, vehicle roll stability control (RSC) schemes, i.e., U.S. Pat. No. 6,324,446, have been proposed to address the issue of friction-induced rollovers. RSC system includes a variety of sensors sensing vehicle states and a controller that controls a distributed brake pressure to reduce a tire force so the net moment of the vehicle is counter to the roll direction.
During an event causing the vehicle to roll, the vehicle body is subject to a roll moment due to the coupling of the lateral tire force and the lateral acceleration applied to the center of gravity of vehicle body. This roll moment causes suspension height variation, which in turn results in a vehicle relative roll angle (also called chassis roll angle or suspension roll angle). The relative roll angle is an important variable that is used as an input to the activation criteria and to construct the feedback pressure command, since it captures the relative roll between the vehicle body and the axle. The sum of the chassis roll angle and the roll angle between wheel axle and the road surface (called wheel departure angle) provides the roll angle between the vehicle body and the average road surface, which is one of the important variables feeding back to the roll stability control module. Trucks, SUVs and cars sometimes are used for carrying heavy loads. For example, a truck full of cargo is loaded in the rear, a trunk of a car may be loaded, and SUV or van may be loaded on its rear. The rear loading may cause the vehicle to have a pitch due to the increased load.
A large rear/trunk load (additional mass) may saturate the lateral forces on the rear axle of the vehicle, making the vehicle more prone to oversteer. In terms of stability, a GWAR (gross weight at rear axle) may cause the vehicle to move with a large side slip angle during some aggressive maneuvers. When the vehicle is sliding at a very large sideslip angle, it gets into nonlinear range of its vehicle dynamics, and sometimes the vehicle could be tripped and rolled over. It is usually hard for the ordinary driver to control and the vehicle dynamics controls have to be activated. Hence, it would be desirable to adjust control authority in stability controls in order to achieve improved performance for a vehicle with large trunk or rear loading.
The large vehicle trunk loading may also have adverse effect on vehicle sensor readings. For example, the trunk loading could cause the vehicle pitch down towards its rear axle. Such loading-induced pitch may cause erroneous readings from a pitch rate sensor, a yaw rate sensor and a longitudinal acceleration sensor. Hence it is desirable to determine such loading-induced pitch misalignment based on the detected trunk or rear loading and to use this information to compensate the sensor signal outputs. Such trunk loading induced pitch misalignment can also be used to conduct vehicle body leveling control and to adjust the orientation of the headlights.